Since I upgraded to Nougat I have developed this issue. I use the option to set my lock screen wallpaper to rotate between 30 selected images from my photos. This works for a few hours. Everytime I look at my lock screen its a different image. Then it stops alternating. I have to go in and select a new batch of photos. It then works for a few more hours. It never stops on the same photo. Anybody else see this happening?